The present invention is directed generally to a fiber optic isolator, and more particularly to a fiber optic isolator for fiber optic systems operating at multiple wavelengths.
Optical fibers find many uses for directing beams of light between two points. Optical fibers have been developed to have low loss, low dispersion, and polarization maintaining properties and can also act as amplifiers. As a result, optical fiber systems find widespread use, for example in optical communication applications.
It is not uncommon for an optical fiber system to support the transport of light at two or more wavelengths. For example, the communications signal propagating along the fiber may have a wavelength of, or be within a wavelength range centered at, about 1.55 xcexcm, while a diagnostic signal may also be sent along the fiber, having a wavelength of approximately 1.3 xcexcm. The diagnostic signal may be, for example, an optical time domain reflectometry (OTDR) signal. Other wavelengths that may be used in the same fiber as the communications signal include a pump signal for pumping an optical amplifier. For example, where the optical signal is at about 1.55 xcexcm, the pump signal may be at about 980 nm for pumping an erbium-doped fiber amplifier, or at about 1.48 xcexcm for pumping a fiber Raman amplifier.
It is common to isolate a fiber signal source from a fiber amplifier by placing an isolator between the two. However, the isolator may introduce loss to the other wavelength component propagating within the fiber. For example, an isolator positioned between the transmitter and a fiber amplifier transmits both the optical communications signal and the OTDR signal in the forward direction. In the reverse direction, the isolator introduces large losses for the optical communications signal. However, the isolator also introduces significant losses for the OTDR signal in the reverse direction, which interferes with the ability to use OTDR as an effective diagnostic tool in a fiber system.
Therefore, there is a need to provide an isolator that is effective at introducing high losses at one wavelength in the reverse direction, but which introduces little loss to a second wavelength in the reverse direction.
In other situations, it may be desired to provide isolation at two wavelengths. However, the bandwidth over which an isolator is effective is limited. Where the two wavelengths are separated by more than the effective bandwidth of the isolator, only one of the wavelengths is isolated effectively.
Therefore, there is a need for a fiber optic isolator that can operate effectively for two wavelengths having a relatively wide separation.
Generally, the present invention relates to an isolator device for use in fiber optic systems that operate with light at more than one wavelength. The isolator device may be inserted anywhere within the fiber network. One particular embodiment of the invention permits the separation of the wavelengths so that an optical isolator module can operate on that separated wavelength without operating on the other wavelength component or components. The different wavelengths may then be recombined. In another embodiment of the invention, different wavelengths may be combined into a single fiber, with an optical isolator module being disposed to operate on one of the wavelengths.
One particular embodiment of the invention is a fiber optic isolator device having a first optical fiber optically coupled to transmit light at first and second wavelengths along a first optical path. A wavelength separator is disposed on the first optical path and is adapted to direct light at the first wavelength along a second optical path and light at the second wavelength along a third optical path different from the second optical path. A wavelength combiner is optically coupled to combine light propagating along the second and third optical paths into a fourth optical path and a second optical fiber optically coupled to the fourth optical path. A first optical isolator module is disposed along the second optical path between the wavelength separator and the wavelength combiner to transmit light at the first wavelength passing from the first fiber to the second fiber, and to substantially block light at the first wavelength from passing from the second fiber to the first fiber.
Another embodiment of the invention is a fiber optic device that has wavelength separating means for separating a light beam into a first light beam containing light at a first wavelength and a second light beam containing light at a second wavelength different from the first wavelength, the first and second beams respectively propagating along first and second beam paths. Optical isolating means is disposed on the first beam path for passing light in the first wavelength from the wavelength splitting means to the wavelength combining means, and for blocking light at the first wavelength from passing from the wavelength combining means to the wavelength splitting means. The device also includes wavelength combining means for combining light propagating in the first direction along the first beam path, and light propagating in the first direction along the second beam path into a single output beam.
Another embodiment of the invention is a fiber optic device that has first and second optical fibers optically coupled via first and second optical paths respectively to a wavelength combiner. Light at a first wavelength from the first optical fiber is combined with light at a second wavelength from the second fiber at the wavelength combiner to form a combined output beam. A third optical fiber is coupled via a third optical path to receive the combined output beam from the wavelength combiner. A first optical isolator module is positioned on the first optical path to pass light at the first wavelength from the first optical fiber to the wavelength combiner, and to substantially block light at the first wavelength from passing from the wavelength combiner to the first optical fiber.
In another embodiment of the invention, a fiber optic device includes a first optical fiber optically coupled via a first optical path to a wavelength separator to transmit light to the wavelength separator. The wavelength separator is arranged to separate light received from the first optical fiber into components at first and second wavelengths. A second optical fiber is coupled via a second optical path to the wavelength separator to receive light at the first wavelength. A third optical fiber is coupled via a third optical path to the wavelength separator to receive light at the second wavelength. A first isolator module is positioned on the second optical path to transmit light at the first wavelength from the wavelength separator to the second optical fiber and to substantially block transmission of light at the first wavelength from the second optical fiber to the wavelength separator.